Method and device for detecting undesired matter in eggs

ABSTRACT

Described is a method for determining whether a brown egg contains undesired matter such as blood. In two wavelength ranges the transmission of the egg is examined, one of those wavelength ranges corresponding to an absorption peak of blood. The transmission signal of the other wavelength range is corrected with a fixed fraction γ to correct for the egg being brown.

This invention relates to a method for detecting the presence ofundesired matter in an egg as described in the preamble of claim 1. Sucha method is generally known in practice and is based on the principle ofcolor spectrum photometry. Although the present invention is generallyapplicable for detecting undesired matter in general, the presentinvention is of interest in particular for detecting the presence ofblood in eggs, for which reason the present invention will be describedhereinbelow for such an exemplary application.

In practice, it may happen that an egg intended for consumption, forinstance a chicken egg, contains blood. Although the presence of bloodis, in principle, harmless, the consumer generally does not find thepresence of blood a pleasant sight. For this reason, egg-processingcompanies generally entertain the desire to supply “pure” eggs only,that is, eggs with as little undesired matter, such as blood, aspossible. This implies there is a need for detection equipment todetermine whether blood is present in an egg. Such detection equipmentis coupled to sorting equipment to remove, during the sorting andpacking of eggs, the unsuitable eggs, that is, the eggs that containundesired matter such as blood.

Naturally, such detection equipment should be non-destructive. Awell-proven detection method for detecting the presence of blood relieson the fact that an egg is semi-transparent, and is based on theabsorption characteristics of eggs and blood. Blood has a strongabsorption line at 577 nm; a normal egg has a much lower absorption atthis wavelength, and the absorption characteristic of a normal egg isvirtually flat in this wavelength range. By directing light at an eggand measuring the amount of transmitted light at 577 nm, the presence ofblood can in principle be determined. However, the light, when passingthrough the egg, will be considerably weakened by the egg itself, andthe extent of weakening can vary from one egg to another: it dependsinter alia on the thickness of the egg. To correct for the extent ofabsorption/weakening by the egg itself, the amount of transmitted lightis also measured in a narrow wavelength band at some distance from theabsorption line referred to; in practice, a wavelength distance of 20 nmis used, and this reference measurement is carried out at approximately597 nm. The result of the measurement at 577 nm can be corrected for theresult of the measurement at 597 nm, to thereby obtain a measuringsignal that depends substantially exclusively on the absorption byblood.

In practice, this method has proven to yield good results. Even eggsthat contain only minute amounts of blood can be detected with a highprobability, while the probability that a bloodless egg is falselyrejected is particularly low.

The good results referred to, however, have so far applied to white eggsonly. In colored eggs, the results are less good, because the coloringof the shell plays a role. In particular, the measuring method referredto has been found to be less reliable in brown eggs. The reason for thisreduced reliability has been found to reside in the fact that the shellof brown eggs itself exhibits an absorption in the range of 577 nm. Thismakes it difficult to discriminate between absorption caused by bloodand absorption caused by the brown shell.

It is therefore an object of the present invention to make the knownblood detection method suitable for examining brown eggs as well.

In particular, the object of the present invention is to provide arelatively simple method which enables determining the presence of bloodin brown eggs with great accuracy.

More particularly, the object of the present invention is to provide amethod for processing the measuring signals that are provided by astandard detection device, without requiring modification of such astandard detection device.

To that end, the method according to the invention has the features asdescribed in the characterizing clause of claim 1.

These and other aspects, features and advantages of the presentinvention will be clarified by the following description of a preferredembodiment of a method and device according to the invention, withreference to the drawing, in which:

FIG. 1 schematically illustrates the principle of blood detection ineggs;

FIG. 2 schematically shows a blood detection device;

FIG. 3A is a flow diagram illustrating a white-calibration procedure;

FIG. 3B is a flow diagram illustrating a brown-calibration procedure;

FIG. 4 is a flow diagram illustrating a first example of a measuringprocedure according to the present invention; and

FIG. 5 is a flow diagram illustrating a second example of a measuringprocedure according to the present invention.

FIG. 1 illustrates the principle of blood detection in eggs, which isknown per se. An egg 3 to be examined is subjected to a first lightradiation L1 having a first predetermined wavelength λ1, coming from alight source 1, and the radiation T1 transmitted by the egg 3 at thiswavelength is received by a detector 2, which provides a firstelectrical signal S1 which is representative of the intensity of thereceived first transmission radiation T1. Similarly, a second electricalsignal S2 is provided, which is representative of the received secondtransmission radiation T2 at a second predetermined wavelength λ2. Thesetwo signals S1 and S2 are presented to a signal processing device 10,which on the basis of those signals decides whether or not the egg 3under examination contains blood. In practice, the wavelengths used areapproximately 597 nm (λ1) and 577 nm (λ2), but other wavelengths are, ingeneral, also conceivable.

In FIG. 1, for the sake of clarity, the light source 1, the egg 3, andthe detector 2 are depicted twice. It is indeed possible to use twodifferent light sources, each transmitting only one of the wavelengthsmentioned, and to use two different light sources, each providing onlyone of the electrical signals mentioned. It is also possible, however,that the two electrical signals S1 and S2 are provided by one and thesame detector 2, which is sensitive to at least both wavelengths λ1 andλ2. Also, the light Li and the light L2 can originate from one and thesame light source 1, which generates light containing at least bothwavelengths λ1 and λ2. To obtain the first electrical signal S1, a firstfilter (not shown for the sake of simplicity) can be placed in the lightpath, either between the light source 1 and the egg 3, or between theegg 3 and the detector 2, which first filter is designed to transmitsubstantially exclusively the first wavelength λ1. Similarly, the secondelectrical signal S2 can be obtained by making use of a second filter,which is designed to transmit substantially exclusively the secondwavelength λ2.

Naturally, other measuring arrangements are also possible, as will beclear to one skilled in the art. In a particular embodiment, lightcontaining both wavelengths λ1 and λ2 is aimed at the egg 3 and afterpassing through the egg 3 is received by a detector with two detectionchannels which are sensitive to the respective wavelengths.

Generally, it holds that the combination of the signals S1 and S2 isrepresentative of the absorption characteristic of the egg 3 in therange 577-597 nm. If the intensity of the light L1 and L2 emitted by thelight source is denoted I(L1) and I(L2), respectively, and theabsorption coefficient of an egg at the wavelengths λ1 and λ2 is denotedα1 and α2, respectively, the magnitude of the electrical detectorsignals S1 and S2 can be written as f1·(1−α1)·I(L1) and f2·(1−α2)·I(L2),where f1 and f2 are proportionality factors expressing inter alia thesensitivity of the detector to the wavelengths λ1 and λ2. Theabove-mentioned combination of the signals S1 and S2 can be expressed,for instance, by defining a state parameter M which is a function of acombination of S1 and S2, for instance M=S1/S2 or M=S1−S2. Hereinafter,the invention will be further elaborated under the assumption that thestate parameter is defined on the basis of a differential signal betweenthe detector signals; it will be clear to one skilled in the art how thepresent invention can be implemented on the basis of a coefficientsignal.

For an egg without blood, the transmission characteristics (andabsorption characteristics) at the two wavelengths λ1 and λ2 arevirtually identical to each other, and any differences in thosecharacteristics will be virtually the same for different eggs withrespect to each other. Although the values of S1 and S2 can vary forindividual eggs, for instance depending on the size of the eggs, theforegoing means that the state parameter M=S1−S2 for bloodless whiteeggs will be substantially equal to zero or will, at most, have a smallvalue which will, in principle, be the same for all bloodless whiteeggs. This value will be designated hereinafter as reference state valueM_(white,0).

Because blood has a narrow absorption peak at approximately 577 nm, witha peak width of approximately 10 nm, it holds for a white egg containingblood that the second absorption coefficient α2 will be considerablygreater than if the egg did not contain any blood, while for the firstabsorption coefficient al the presence or absence of blood will makelittle difference, if any. This means that the absolute value of thestate parameter M will then be significantly greater than theabove-mentioned “reference state value” M_(white,0). In white eggs, thisis a reliable indication of the presence of blood, and the magnitude ofthe difference M-M_(white,0) is a reliable measure of the amount ofblood in the egg in question. To determine whether the amount of bloodin an egg is acceptable or not, a state threshold ΔM can be defined, andM−M_(white,0) can be compared with this predefined state threshold ΔM;if M−M_(white,0)<ΔM, the amount of blood is acceptable.

As for an egg with a brown shell, the matter is more complicated,because the brown shell also has an absorption peak at λ2. Then the meregiven that the state parameter M is significantly greater than theabove-mentioned reference state value M_(white,0) is not a reliableindication of the presence of blood. The present invention provides asolution to this problem, which will be described in the following.

FIG. 2 diagrammatically shows a blood detection device 20. It comprisesa conveying device 21 for eggs 3, for instance a conveyor or the like.Arranged along the conveying device 21 is a detection station 22, whichcomprises, for instance, a light source 1 and a detector 2, asillustrated in more detail in FIG. 1. The blood detection device 20further comprises a signal processing device 10 which receives thesignals S1 and S2 from the detector 2. Further, a removal device 23 isprovided, which is arranged to remove eggs from the conveying device 21under the control of the signal processing device 10.

In the foregoing, it has been mentioned that the reference state valueM_(white,0) is very small. To eliminate any instrumentation differences,it is preferably ensured that M_(white,0) is substantially equal tozero. To that end, the blood detection device 20 is adjusted in awhite-calibration procedure, such that in bloodless white eggs the twosignals S1 and S2 are substantially equal to each other; in other words,M_(white,0) is made equal to zero. This can be accomplished in variousways. Firstly, it is possible to set the light strength of the lightsource 1 for generating L1 and/or the light strength of the light source1 for generating L2, such that upon detection it is found that S1=S2.Secondly, it is possible, for instance, to multiply in the signalprocessing device 10 one of the received signals S1, S2 by a firstcorrection factor c, such that c·S1=S2 and S1=c·S2, respectively.

Hereinafter, it will be assumed that in the calibration the signalprocessing device 10 multiplies the first detector signal S1 by thefirst correction factor c, such that c·S1=S2. It is noted that thiscorrection can be carried out through hardware, by an amplifier with anadjustable amplification factor, but it is also possible to carry outthis correction through software in the signal processing device 10.

The above-mentioned white-calibration procedure is illustrated in FIG.3A. A bloodless white egg is subjected to the radiation L1 and L2, andthe signals S1 and S2 are measured (step 101). Then the first correctionfactor c is determined as c=S2/S1 (step 102). If desired, the steps 101and 102 can be repeated for several eggs, and the obtained values of ccan be averaged.

FIG. 4 illustrates an example of the actual measuring procedureaccording to the present invention. First, it is determined whether anegg to be examined is a white or a brown egg. This can be accomplishedin different ways. Thus, it is possible, for instance, to employ acolor-sensitive detector, which is known per se. In a preferredembodiment of the method according to the present invention, however,use is made of the signals S1 and S2 provided by the detectors 2, sothat utilization of a separate color-sensitive detector is not needed.The fact is that it has been found that in brown eggs the absorptioncoefficients α1 and α2 are considerably greater than in white eggs, sothat the provided signals S1 and S2 have a considerably smallerintensity, making it possible to discriminate between brown and whiteeggs on the basis of those signals S1 and S2.

According to the present invention, therefore, in a preferred embodimentof the white-calibration procedure, the magnitude of the signal S1 asobtained from bloodless white eggs is fixed as a reference S0 (step 103,FIG. 3A), which will hereinafter be referred to by the term“white-reference”. If desired, step 103 can be repeated for multipleeggs, and the obtained values of S0 can be averaged.

In the actual measuring procedure on an unknown egg (FIG. 4) the signalsS1 and S2 are measured (step 201). To determine whether this unknown eggis a white or a brown egg, in a preferred embodiment of the measuringprocedure, the measured signal S1 is compared with the above-mentionedwhite-reference S0 (step 202). If S1 is smaller than S0 to a sufficientextent, for instance S1<75% of S0, it is decided that the egg underexamination is a brown egg; if not, it is decided that the egg underexamination is a white egg (step 203).

If it has been decided that the egg under examination is a white egg,the measuring signals S1 and S2 are further processed in a conventionalmanner to detect the presence of blood. In step 204, a corrected stateparameter M_(c) is computed as M_(c)=cS1−S2. In step 205 M_(c) iscompared with zero. If M_(c) is significantly greater than zero, it isconcluded that the egg in question contains blood; if not, it isconcluded that the egg in question does not contain any blood (step206). On the basis of this outcome, the signal processing device 10 cancontrol the removal device 23 to remove the blood-containing egg.

If, however, it is decided that the egg under examination is a brownegg, first a correction is performed on the measuring signals S1 and/orS2 to correct for the shell being brown (step 207). It has been foundthat such a correction, if desired, can be carried out in the samemanner for all brown eggs, regardless of the degree of brownness, shellthickness, etc. The magnitude of the correction has likewise beenpriorly determined, viz. in a calibration procedure which will bedesignated as “brown-calibration procedure”, utilizing bloodless browneggs.

The brown-calibration procedure is illustrated in FIG. 3B. A bloodlessbrown egg is subjected to the radiation L1 and L2, and the signals S1and S2 are measured (step 111). Then the signal S1 is corrected with thefirst correction factor c to provide a corrected signal S1′ according tothe formula S1′=c·S1 (step 112). As mentioned before, brown eggs exhibitan absorption at 577 nm, so that for brown eggs S1′ will be greater thanS2. The differential signal ΔS is determined according to the formulaΔS=S1′−S2 (step 113). Then this differential signal ΔS is expressed as afraction of the corrected signal S1′, according to the formula ΔS=γ·S1′,that is, the fraction γ is computed according to the formula γ=ΔS/S1′(step 114). Alternatively, the steps 112-114 can be combined into asingle step in which the fraction y is determined according to theformula γ=(c·S1−S2)/c·S1. If desired, the steps 111-114 can be repeatedfor multiple eggs, and the obtained values of γ can be averaged.

In the eventual measuring procedure, if in step 203 it has been decidedthat the egg under examination is a brown egg, the corrected stateparameter M_(c) is computed as M_(c)=(1−γ) c·S1−S2 (step 207). Then, ina comparable manner to that described in respect of white eggs, M_(c) iscompared with zero, that is, the measuring procedure proceeds, afterstep 207, with step 205 already mentioned. Accordingly, it holds thatfurther the following method step is carried out: (f) only for browneggs, the first and second measuring signal are corrected relative toeach other with a fraction γ. This can be carried out by a correction ofthe first signal S1 relative to the second signal, a correction of thesecond signal relative to the first signal, or a correction of the firstand second signal whereby the signals are corrected relative to eachother. In this example, it holds in particular that an (S1) of themeasuring signals is corrected with the fraction γ. Because according tothe invention, the measuring signals S1 and S2 must be correctedrelative to each other with a fraction 65 , it is, of course, alsopossible to define M_(c) in step 207 as M_(c)=(1−γ)·c·E·S1−ES2, where Eis a number not equal to zero. E can be chosen, for instance, to beequal to (1−γ)⁻¹. In that case, only the signal S2 needs to be correctedwith the fraction γ. In that case, it holds that M_(c)=cS1−(1−γ)S2 andtherefore only the second measuring signal is corrected. E can also beselected to be equal to (1−γ)^(½), so thatM_(c)=(1−γ)^(+½)·cS−(1−γ)^(−½)·S2. Both are then subjected to a mutuallydifferent correction and are then corrected relative to each other.

With the above-described measuring procedure it has been found possibleto reliably detect even minute blood spots in brown eggs. Surprisingly,it has been found that the fraction γ can be a substantially constantvalue which had good utility in brown eggs, regardless of theirdiameter, the thickness of the shell or the darkness of the shell, andthat in all of these cases the above-defined corrected state parameterM_(c) is a reliable indicator of the presence of blood.

It will be clear to one skilled in the art that the scope of protectionof the present invention as defined by the claims is not limited to theembodiments represented in the drawings and discussed, but that it ispossible to alter or modify the represented embodiments of the methodaccording to the invention within the scope of the inventive concept.Thus it is possible, for instance, to skip step 207 and, instead of step205, to compare the corrected measuring signal (1−γ)·c·S1 with S2.

Also, as stated, it is possible to compare a corrected signal S2 withS1. Moreover, a fraction γ′ can be defined as γ′=1−γ. In the descriptiongiven hereinabove and in the drawing, γ can then be replaced throughoutwith 1−γ′. The fraction γ′ can then be determined in a brown-calibrationaccording to the formula 1−γ′=ΔS/S′ (step 114). If the steps 112-114 arecombined into a single step, γ′ can be determined in a brown-calibrationaccording to the formula 1−γ′=(c·S1−S2)/cS1. It follows that γ′=S2/cS1in the brown-calibration. If γ′ has thus been determined, the signals S1and S2 can be corrected relative to each other with the fraction γ. Thiscan be carried out, for instance, by multiplying the signal S1 by thefraction γ′. It is also possible to multiply the signal S2 by thefraction (γ′)⁻¹. Naturally, it is also possible to multiply the signalS1 by E and the fraction γ′ and to multiply the signal S2 by E, with Ebeing a random number not equal to zero. In each of these cases, itholds that the signals S1 and S2 are corrected relative to each otherwith the fraction γ′. In step 207, M_(c) can then be defined asM_(c)=cγ′·S1−S2, M_(c)=c·S1−γ′⁻¹·S2 or M_(c)=c·γ′·E·S1−E·S2,respectively. In the latter case, M_(c) can optionally be defined instep 204 as M_(c)=c·E·S1−E·S2.

In FIG. 5, a second example of a measuring method according to theinvention is shown, which comprises a further refinement with respect tothe method discussed with reference to FIG. 4. According to the methodto be described with reference to FIG. 5, an egg with blood can bedistinguished from an egg without blood with a further increased chanceof success. The method also works well in, on the one hand,thick-shelled white versus thin-shelled brown eggs and, on the otherhand, in light brown eggs and dark brown eggs. Again, in step 301 thefirst signal S1 and the second signal S2 are determined. Also, in a step302 it is determined according to a predetermined criterion whether theegg under examination is a white egg, a light brown egg or a dark brownegg. In this example, the light brown eggs are separated from the darkbrown eggs using a color camera, such as, for instance, twosemiconductor diodes that are sensitive to green and red light,respectively. In this example, moreover, using the same camera, it isdetermined whether the egg is a white egg. Accordingly, in this example,using the camera, it is determined whether the egg is a white, a lightbrown or a dark brown egg.

If the egg is a white egg, a step 303 is carried out which is entirelyanalogous to the step 204. If the egg is a light brown egg, a step 304is carried out which corresponds to step 207. The fraction γ1, however,is a fraction which has been determined in a light brown-calibrationprocedure for light brown eggs. All this is entirely analogous to themanner discussed for brown eggs with reference to FIG. 4. If the egg isa dark brown egg, a step 305 is carried out which is again equal to thestep 207 discussed with reference to FIG. 4. In this case, however, afraction γ2 is used for dark brown eggs, which has been obtainedentirely analogously in a dark brown-calibration procedure for darkbrown eggs, as has been discussed for brown eggs with reference to FIG.4. Accordingly, the first and second measuring signal for light browneggs are corrected relative to each other with a first fraction γ1 forlight brown eggs, and the first and second measuring signal for darkbrown eggs are corrected relative to each other with a second fractionγ2 for dark brown eggs. Accordingly, the fraction γ1 has been determinedfor light brown eggs in a light brown-calibration procedure on the basisof at least one bloodless light brown egg. Further, the fraction γ2 fordark brown eggs has been determined in a dark brown-calibrationprocedure on the basis of at least one bloodless dark brown egg. Inaddition, the first and second measuring signal for all eggs arecorrected relative to each other with the first correction factor c,which has been determined in the white-calibration procedure on thebasis of at least one bloodless white egg. Also, in step 304 for lightbrown eggs the second measuring signal S2 is compared with the firstmeasuring signal corrected relative to the second measuring signal,(1−γ1)·c·S1, where c is the first correction factor satisfying c=S2/S1in the case of a bloodless white egg. Here, the fraction γ1 for lightbrown eggs satisfies γ1=(c·S1−S2)/c·S1 in the case of a bloodless lightbrown egg. For dark brown eggs, it holds that the second measuringsignal S2 is compared with the first measuring signal corrected relativeto the second measuring signal, (1−γ2)·c·S1, where c is theabove-mentioned first correction factor and where said fraction y2 fordark brown eggs satisfies γ2=(c·S1−S2)/c·S1 in the case of a bloodlessdark brown egg. Again, in the white-calibration procedure a bloodlesswhite egg is subjected to the radiation L1 and L2, the signals S1 and S2are measured, and the first correction factor c is defined as c=S2/S1.Further, in the light brown-calibration procedure, a bloodless lightbrown egg is subjected to the radiation L1 and L2, the signals S1 and S2are measured, and the fraction γ1 is determined according to the formulaγ1=(c·S1−S2)/c·S1, and in the dark brown-calibration procedure abloodless dark brown egg is subjected to the radiation L1 and L2, thesignals S1 and S2 are measured, and the fraction γ2 is determinedaccording to the formula γ2=(c·S1−S2)/c·S1.

When the value of M_(c) in step 303, 304, or 305 has been determined, itis compared with 0. All this is carried out entirely analogously to themanner discussed for FIG. 4 with reference to step 205. Again, next, instep 307, entirely analogously to step 206 according to FIG. 4, it isdetermined whether the value of M_(c) is significantly greater than 0.If this is the case, it is concluded that blood is present in the egg.If this is not the case, it is concluded that no blood is present in theegg.

It will be clear that steps 301 and 302 can be carried out in a randomorder. Further, it is possible to skip steps 303, 304 and 305 andinstead, in step 306, to compare the corrected measuring signal cS1,cS1(1−γ1) or cS1(1−γ2) with S2. Also, again a fraction γ1′ can bedefined as γ1′=1−γ1 and a fraction γ2′ can be defined as γ2′=1−γ2, allentirely analogously to the manner as discussed with reference to FIG.4. Also, the signal S1 and the fractions γ1′ and γ2′ can then bemultiplied again by the factor E mentioned earlier.

Such variants are each understood to fall within the scope of theinvention.

What is claimed is:
 1. A method for detecting the presence of undesiredmatter in an egg, comprising the steps of: (a) irradiating the egg to beexamined with radiation which comprises at least two predeterminedwavelength ranges; (b) providing a first measuring signal S1representative of the amount of radiation in a first wavelength of saidtwo predetermined wavelength ranges transmitted by the egg; (c)providing a second measuring signal S2 representative of the amount ofradiation in a second wavelength of said two predetermined wavelengthranges by the egg; (d) automatically determining whether an egg to beexamined is a white or brown egg; (e) only for brown eggs: correctingthe first and second measuring signals relative to each other with atleast one brown egg correction factor correcting for the shell beingbrown to produce corrected first and second measuring signals; (f)comparing the first measuring signal S1, with the second measuringsignal S2 as corrected relative to each other in step (e); and. (g)determining the presence of undesired matter in the brown egg to beexamined on the basis of the outcome of said comparison in step (f). 2.A method according to claim 1, characterized in that only for browneggs, one of said two measuring signals is corrected with the at leastone brown egg correction factor based on mathematical fraction of thefirst measuring signal S1.
 3. A method according to claim 1,characterized in that the at least one brown egg correction factor ismaintained constant for all brown eggs.
 4. A method according to claim1, characterized in that the at least one brown egg correction factorhas been determined in a brown-calibration procedure based on at leastone bloodless brown egg.
 5. A method according to claim 4, wherein, inthe brown-calibration procedure, a bloodless brown egg is subjected tothe radiation, the signals S1 and S2 are measured, and the brown eggcorrection factor comprises γ determined according to the formulaγ=(c·S1−S2)/c·S1, and where c is determined as c=S2/S1 and wherein S1and S2 are determined in a white-calibration procedure wherein abloodless white egg is subjected to the radiation and the signals S1 andS2 are measured.
 6. A method according to claim 1, characterized in thatthe second measuring signal S2 is obtained in a wavelength range whereblood has an absorption peak, and wherein the first measuring signal S1is obtained at a wavelength which is located at a short distance next tosaid absorption peak.
 7. A method according to claim 1, characterized inthat further according to a predetermined criterion, light brown eggsare separated from dark brown eggs, while the first and second measuringsignals for light brown eggs are corrected relative to each other with alight brown egg correction factor and the first and second measuringsignals for dark brown eggs are corrected relative to each other with adark brown egg correction factor, the light brown egg correction factordiffering from the dark brown egg correction factor.
 8. A methodaccording to claim 7, characterized in that the light brown eggs areseparated from dark brown eggs using a color-sensitive detector.
 9. Amethod according to claim 8, characterized in that using thecolor-sensitive detector, it is determined whether an egg is a white,light brown or dark brown egg.
 10. A method according to claim 7,characterized in that the light brown egg correction factor has beendetermined in a light brown-calibration procedure based on at least onebloodless light brown egg and the dark brown egg correction factor hasbeen determined in a dark brown-calibration procedure based on at leastone bloodless dark brown egg.
 11. A method according to claim 10,characterized in that in the light brown-calibration procedure abloodless light brown egg is subjected to the radiation, the signals S1and S2 are measured, and the light brown egg correction factor comprisesγ1 determined according to the formula γ1=(c·S1−S2)/c·S1, and in thedark brown-calibration procedure a bloodless dark brown egg is subjectedto the radiation, the signals S1 and S2 are measured, and the dark brownegg correction factor comprises γ2 determined according to the formulaγ2=(c·S1−S2)/c·S1, and where c is determined as c=S2/S1 and wherein S1and S2 are determined in a white-calibration procedure wherein abloodless white egg is subjected to the radiation and the signals S1 andS2 are measured.
 12. A method according to claim 7, characterized inthat for light brown eggs, the second measuring signal S2 is comparedwith a first measuring signal corrected relative to the second measuringsignal, (1−γ1) c·S1, where c is a correction factor which satisfiesc=S2/S1 in the case of a bloodless white egg, and γ1 is the light brownegg correction factor having a value which satisfies γ1=(c·S1−S2)/c·S1in the case of a bloodless light brown egg; while for dark brown eggs,the second measuring signal S2 is compared with a first measuring signalcorrected relative to the second measuring signal, (1−γ2) c·S1, where cis said correction factor and γ2 is the dark brown egg correction factorhaving a value which satisfies γ2=(c·S1−S2)/c·S1 in the case of abloodless dark brown egg.
 13. A method according to claim 1,characterized in that to determine whether an egg to be examined is awhite or a brown egg, the first measuring signal S1 is compared with awhite-reference.
 14. A method according to claim 13, wherein, in awhite-calibration procedure, a bloodless white egg is subjected to theradiation, the signals S1 and S2 are measured, and the white-referenceis defined as the value of the first measuring signal S1.
 15. A methodaccording to claim 1, wherein the first and second measuring signal forall eggs are corrected relative to each other with a correction factorwhich has been determined in a white-calibration procedure based on atleast one bloodless white egg.
 16. A method according to claim 1,characterized in that the second measuring signal S2 is compared with afirst measuring signal corrected relative to the second measuringsignal, (1−γ) c·S1, where C is a correction factor which satisfiesc=S2/S1 in the case of a bloodless white egg, and γ is the brown eggcorrection factor having a value which satisfies γ=(c·S1−S2)/c·S1 in thecase of a bloodless brown egg.
 17. A method according to claim 16,characterized in that in a white-calibrated procedure, a bloodless whiteegg is subjected to the radiation, the signals S1 and S2 are measured,and the correction factor c is determined as c=S2/S1.
 18. A methodaccording to claim 1, wherein the second wavelength is approximatelyequal to 577 nm and wherein the first wavelength is approximately equalto 597 nm.
 19. A detection device for detecting the presence ofundesirable matter in an egg, said method comprising: at least one lightsource for irradiating the egg to be examined with radiation whichcomprises at least two predetermined wavelength ranges; at least onedetector for providing a first measuring signal S1 representative of theamount of radiation in a first wavelength of said two predeterminedwavelength ranges transmitted by the eggs and for providing a secondmeasuring signal S2 representative of the amount of radiation in asecond wavelength of said two predetermined wavelength rangestransmitted by the eggs; and a signal processing device of which asignal input is coupled for receiving said first and second measuringsignals, wherein said signal processing device is arranged for:comparing the first measuring signal with the second measuring signalfor automatically determining the presence of undesired matter in theegg to be examined, regardless of egg color, on the basis of the outcomeof said comparison, wherein the detection device is adapted forautomatically determining whether or not an egg is a brown egg andwherein the signal processing device is further adapted for correctingthe first and second measuring signals relative to each other with atleast one brown egg correction factor correcting for the shell beingbrown.
 20. The device according to claim 10, further comprising awhite-calibration procedure wherein the signal processing device isarranged to compute the correction factor c as c=S2/S1, wherein S1 andS2 are the signals from a white egg.
 21. The device according to claim19, further comprising a brown-calibration procedure wherein the signalprocessing device is arranged to determine the brown egg correctionfactor comprising γ according to the formula γ=(c·S1−S2)/c·S1 wherein S1and S2 are the signals from a brown egg and c is defined as S2/S1wherein S1 and S2 are signals from a bloodless white egg.
 22. The deviceaccording to claim 19, further comprising a light brown-calibrationprocedure wherein the signal processing device is arranged to determinea light brown egg correction factor comprising γ1 according to theformula γ1=(c·S1−S2)/c·S1 wherein S1 and S2 are signals for a lightbrown egg and c is a correction factor defined as S2/S1 where S1 and S2are signals from a bloodless white egg, and a dark brown-calibrationprocedure to determine a dark egg correction factor comprising γ2according to the formula γ2=(c·S1−S2)/c·S1 wherein S1 and S2 are signalsfrom a dark brown egg, where c is a correction factor defined as S2/S1wherein S1 and S2 are the signals from a bloodless white egg.
 23. Thedevice according to claim 19, wherein the signal processing device isarranged to determine in an actual measuring procedure whether an egg tobe examined is a white, light brown or dark brown egg, and if the egg tobe examined is a light brown egg, to compute the value (1−γ1)·c·S1, andif the egg to be examined is a dark brown egg, to compute the value(1−γ2)·c·S1, where c is a correction factor defined as S2/S1 wherein S1and S2 are the signals from a bloodless white egg, γ1 is a light brownegg correction factor and γ2 is a dark brown egg correction factor. 24.A method for detecting the presence of undesired matter in an egg,comprising the steps of: (a) irradiating the egg to be examined withradiation which comprises at least two predetermined wavelength ranges;(b) providing a first measuring signal S1 representative of the amountof radiation in a first wavelength of said two predetermined wavelengthranges transmitted by the egg; (c) providing a second measuring signalS2 representative of the amount of radiation in a second wavelength ofsaid two predetermined wavelength ranges transmitted by the egg; (d)automatically determining whether an egg to be examined is a white orbrown egg; (e) only for brown eggs: (1) correcting the first and secondmeasuring signals relative to each other with a calibration factor toprovide corrected first and second measuring signals, and (2) correctingsaid corrected first and second measuring signals further with at leastone brown egg correction factor to produce brown egg corrected first andsecond measuring signals; (f) comparing the first signal S1 with thesecond measuring signal S2, as corrected relative to each other by(e)(1) or (e)(2); and (g) determining the presence of undesired matterin the brown egg to be examined on the basis of the outcome of saidcomparison in step (f).
 25. A method for detecting the presence ofundesired matter in an egg, comprising the steps of: (a) irradiating theegg to be examined with radiation which comprises at least twopredetermined wavelength ranges; (b) providing a first measuring signalS1 representative of the amount of radiation in a first wavelength ofsaid two predetermined wavelength ranges transmitted by the egg; (c)providing a second measuring signal S2 representative of the amount ofradiation in a second wavelength of said two predetermined wavelengthranges transmitted by the egg; (d) automatically determining whether anegg to be examined is a white or brown egg; (e) correcting the first andsecond measuring signals relative to each other for all eggs with acalibration factor; (f) only for brown eggs: further correcting thecorrected first and second measuring signals as corrected in step (e)relative to each other with at least a brown egg correction factorcorrecting to the egg shell being brown; (g) comparing the correctedfirst and second measuring signals for white eggs as obtained in step(e) and comparing the corrected first and second measuring signals forbrown eggs as obtained in step (f); and (h) determining the presence ofundesired matter in the egg to be examined on the basis of saidcomparison in step (g).
 26. A method for detecting the presence ofundesired matter in an egg, comprising the steps of: (a) irradiating theegg to be examined with radiation which comprises at least twopredetermined wavelength ranges; (b) providing a first measuring signalS1 representative of the amount of radiation in a first wavelength ofsaid two predetermined wavelength ranges transmitted by the egg; (c)providing a second measuring signal S2 representative of the amount ofradiation in a second wavelength of said two predetermined wavelengthranges transmitted by the egg; (d) automatically determining whether anegg to be examined is a white or brown egg; (e) for white eggs:correcting the first and second measuring signals relative to each otherwith a first correcting factor to produce corrected first and secondmeasuring signals; (f) for brown eggs: correcting the first and secondmeasuring signals relative to each other with at least one secondcorrection factor which differs from the first correction factor toproduce corrected first and second measuring signals; (g) comparing thefirst and second measuring signal, S1,S2 as corrected in step (e) and(f), respectively; and (h) determining the presence of undesired matterin the egg to be examined on the basis of the outcome of said comparisonin step (g).